Preheat oven to 350°F. Place non-stick foil in the bottom and overhanging sides of a 9 x 13 x 2-inch baking dish, set aside. In medium bowl, stir together flour, baking powder and salt until blended.
In another bowl, beat butter and sugar on medium-high speed until fluffy. Add egg and beat until blended. Add peanut butter, beat until well blended. On low-speed, add in flour and beat just until blended. Stir in vanilla. Spread into pan.
Bake for 30 min. Remove from oven and spread with jam, sprinkle with chopped nuts. Bake additional 5 min. Cool completely.